Safety bars of this type are known in the form of what are referred to as "anti-submarining" bars, their purpose being to prevent the occupant of the seat from sliding underneath the ventral strap of his safety belt and being forced into the upholstery of the seat if the vehicle is subjected to a frontal impact.
Document FR-A-2 747 080 describes an example of a seat in which a safety bar of this type is pivotally mounted on connecting plates and is moved upwards and forwards under the action of a pyrotechnic pre-tensioning device if the vehicle is subjected to a frontal impact. These features prevent the safety bar from impinging on the comfort of the occupant under normal circumstances, yet make it effective when moved into the activated position in the event of an accident.
The disadvantage of this known seat is that when the safety bar is in the set-back position it is located towards the rear of the seat, relatively speaking, at a point where the seat upholstery and the elastic metal layer supporting this upholstery are susceptible to local deformation under the weight of the occupant and may impair or even prevent correct displacement of the safety bar into its activated position in the event of an accident.
This being the case, the safety bar remains locked in a rear position and is unable to fulfil its function which means that the pelvis of the occupant is at risk of digging in as it moves forward underneath the ventral strap of the safety belt when subjected to impact, which can cause serious injury to the occupant.